Directivity Assessment of MEMS Microphones in Microphone Array Applications

In this paper, the actual omni-directionality of MEMS-microphones (micro-electro- mechanical system) is studied. Commercially available MEMS-microphones are claimed to be omni-directional but there is no real proof for these statements in the data sheets. In addition, is this statement valid for the whole spectrum in which the microphones operate? And, is there any in uence of the PCB material they are mounted on? To answer these questions, a directivity assessment was performed. The microphones where placed in an anechoic chamber in which the microphones could rotate automatically, with an accuracy of 0.1125 degrees. The obtained measurement results are depicted in several polar plots. This process was repeated for several types of MEMS microphones. With these plots, it is pos- sible to do a graphical comparison between the dierent MEMS-microphones. Apart from individual MEMS-microphones, also a linear array of four micro- phones is measured. Results show the in uence of the nearby PCB-components and give an overview of the overall omni-directionality. In addition to this, we can see in uences of the PCB material itself. The measurement-based assessment was performed at dierent frequencies to derive spectral information. In the follow up of this paper, we aim to improve the used Angle-Of-Arrival (AoA) algorithms by exploiting the possible attenuations on certain angles. This paper will also explore how the omni-directive features could be exploited in cryptographic applications.